There are a wide range of laser beam delivery systems in common use for various purposes, including micro-machining and medical functions. Virtually all such systems for practical purposes employ complex optical systems comprised of mirrors and lenses of various types to shape, focus and guide the beam, and to “fold” the beam path to reduce the mechanical length of the optical system and to thereby allow a physically more compact system. The optical systems of laser beam delivery systems are typically very complex, however, with certain systems, such as UV (ultraviolet) laser ablation systems used for microvia drilling, requiring up to six or more mirrors and a comparable number arraignment of lenses of various types.
One of the major requirements for use of such systems is the alignment of the elements of the optical system to safely deliver a correctly focus and shaped laser beam at the intended target, which typically requires the individual and joint alignment of each optical element in the system. Stated simply, the alignment process requires that the aligner determine for each optical element, such as a mirror, where the beam strikes the optically functional area of the element. The aligner should also preferably be able to determine the shape or pattern of the beam at that point and possibly the relative power of the beam at that point.
This problem further compounded in that the laser beams generated in many laser beam delivery systems, such as ablation systems, are comprised of “invisible” or “non-visible” radiation, that is, radiation that is not visible to the unaided human eye. Such non-visible radiation may include, for example, UV (ultraviolet) radiation or infrared (IR) radiation, and may also include beams comprised of radiation at wavelengths that are in or near the visible spectrum but that because of other characteristics, such as power and beamwidth, are difficult to see and are thereby effectively “non-visible”.
Such beams are also often of relatively high power levels, and are thereby a significant hazard to the eyes of the aligner and user of the system and to any others that may stray into the path of the beam as the aligner, user or bystander may be unaware of a hazard from the beam until damage has been inflicted. This problem is further compounded because it is effectively impossible to align a non-visible radiation system without optical assistance, thereby placing the aligners eye or eyes in the danger zone.
For these reasons, UV systems of the prior art were typically aligned by inserting a piece of white paper into the general and assumed path of the UV beam. White paper typically fluoresces when irradiated with UV radiation, so that a fluorescent spot will appear on the paper indicated the position of the beam, if the paper is in the path of the beam. This method has a number of disadvantages, however. One is that the aligner is exposed to significant levels of scatter radiation, that is, UV radiation reflected from the surface of the paper, which can cause a ‘sun burn” type of injury or even photothalmia, which is effectively a sunburn of the eye tissues. The other problem is that the paper effectively blocks the path of the beam, so that if a mirror, for example, is behind the paper, the location at which the beam strikes the surface of the mirror must be estimated from the location at which the beam strikes the paper. This problem becomes more severe, of course, the greater the distance between the paper and the surface of the mirror and can be reduced by placing the paper closely on the surface of the mirror, which may be a problem in itself due to mechanical constraints and the possibility of smearing the surface of the mirror. Yet another problem with this method is that the laser beam sometimes “burns” the paper, resulting in the deposit of contaminates on the mirror or on other optical elements of the system
A related problem that is common in laser beam delivery systems is the testing and measurement of various critical performance specifications and properties of the various types of optical elements found in a laser beam delivery system, such as F-theta lenses, beam shaping elements and other imaging lenses.
While this problem is present with many different types of optical elements in laser beam delivery systems, one of the most difficult manifestations of the problem arises with F-theta lenses and similar lenses due to the well known variability of the properties of F-theta lenses, even when manufactured under tight specifications and control. As such, the following discussions will use F-theta lenses as an example of the optical elements that may be tested and measured using the apparatus and methods of the present invention, with the understanding that the discussion of F-theta lenses is illustrative rather than limiting and that the apparatus and methods of the present invention are applicable to other forms and types of optical elements.
Because of the complex interactions of the elements of a laser beam delivery system, a test facility capable of simulating a laser beam delivery system for purposes of testing the optical elements of a laser beam delivery system is effectively, in function, structure and operation, an actual laser beam delivery system. Therefore, and according to current methods, most makers of laser beam delivery systems employing, for example, F-theta lenses, determine whether the lenses do in fact meet specifications by placing the lenses into an actual production laser beam delivery system, processing material through the system, and evaluating the resulting material products.
Not only does this method require that the “test facility” be an actual production laser beam delivery system, but the testing itself is complex and very sensitive and subject to variations in the material properties and to variations in the exact test steps and method.
Also, and while the F-theta lens or lenses installed in a laser beam delivery system may be tested under controlled conditions by appropriately trained personnel before the unit is initially shipped to the system user, it will eventually be necessary to replace the original lens or lenses at the user site. This will typically require that a new lens be shipped to the user from the lens maker or from the system maker and there will again be no assurance that the new lens will perform as specified. As a result, the new lens will typically have to be installed at the use site and again tested in the actual beam delivery system under production conditions. Again, the testing is itself complex and very sensitive and subject to variations in the material properties and to variations in the exact test steps and method and, in this instance, must be done at the user site under less controlled conditions and perhaps by personnel that are not as trained and experienced as were available for the original equipment.
At present, a preferred method for reducing these problems is to over-specify the lenses, such as requiring a larger scan field and higher imaging resolution than is actually required, and using the lens at a reduced performance level to thereby increase the probability that the properties of a given lens will fall within the actual system requirements. This method, however, significantly increases the cost of such optical elements, directly by requiring extensive and complex testing procedures under disadvantageous conditions and increasing the performance requirements of the elements beyond that actually needed and indirectly by reducing the manufacturing yield of the elements.
The present invention provides a solution to these and related problems of the prior art